Method - Step 2b: Primary Chords
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In this step, you harmonise the chorale using only primary chords in root position. The idea is to lay down a basic framework that you can then improve in order to make both the bass line and harmony more typical of Bach. Although this basic harmonisation is very crude, you may be surprised by how convicing it sounds.
For each note of the chorale put the bass note and chord label for whichever primary chord fits. Where you have the option of two chords, choose one and, if you wish, put the other in brackets below in case you change your mind later on
The resulting bass line is not supposed to be a beautiful melody and nor is the harmony supposed to be interesting - this is just a starting point for the next step.
This is all more-or-less mechanical and straightforward, except for where phrases begin and end in different keys. In the first phrase above this is not a problem, but in the second phrase (as planned out in the previous step) we need to move from G major to D major.
The best way to move between two closely related keys is to use a pivot modulation. In the example above, the D major chord in the box can be V in G (the old key) AND I in D. This common chord (or pivot) between the two keys makes the transition from one to the other smooth and effective. You can find further notes and a pivot modulation method on the modulation resources page.